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Signing HTTP MessagesOracle500 Oracle ParkwayRedwood ShoresCA94065US+1 415 400 0626mcavage@gmail.comhttp://www.oracle.com/Digital Bazaar203 Roanoke Street W.BlacksburgVA24060US+1 540 961 4469msporny@digitalbazaar.comhttp://manu.sporny.org/Security
HTTPdigital signaturePKI
When communicating over the Internet using the HTTP protocol, it can be
desirable for a server or client to authenticate the sender of a
particular message. It can also be desirable to ensure that the message
was not tampered with during transit. This document describes a way for
servers and clients to simultaneously add authentication and
message integrity to HTTP messages by using a digital signature.
This specification is a joint work product of the
W3C Digital Verification Community Group
and the
W3C Credentials Community Group.
Feedback related to this specification should be sent to
public-credentials@w3.org.
This protocol extension is intended to provide a simple and standard way for
clients to sign HTTP messages.
HTTP Authentication defines Basic and Digest
authentication mechanisms, TLS 1.2
defines cryptographically strong transport layer security, and
OAuth 2.0 provides a
fully-specified alternative for authorization of web service requests. Each of
these approaches are employed on the Internet today with varying degrees of
protection. However, none of these schemes are designed to cryptographically
sign the HTTP messages themselves, which is required in order to ensure
end-to-end message integrity. An added benefit of signing the HTTP message
for the purposes of end-to-end message integrity is that the client can be
authenticated using the same mechanism without the need for multiple
round-trips.
Several web service providers have invented their own schemes for signing
HTTP messages, but to date, none have been standardized. While there
are no techniques in this proposal that are novel beyond the previous art, it
is useful to standardize a simple and cryptographically strong mechanism for
digitally signing HTTP messages.
It is common practice to protect sensitive website API functionality via
authentication mechanisms. Often, the entity accessing these APIs is a
piece of automated software outside of an interactive human session. While
there are mechanisms like OAuth and API secrets that are used to grant
API access, each have their weaknesses such as unnecessary complexity
for particular use cases or the use of shared secrets which may not be
acceptable to an implementer.
Digital signatures are widely used to provide authentication without
the need for shared secrets. They also do not require a round-trip in
order to authenticate the client. A server need only have a mapping between
the key being used to sign the content and the authorized entity to
verify that a message was signed by that entity.
This specification provides two mechanisms that can be used by a server
to authenticate a client. The first is the 'Signature' HTTP Authentication
Scheme, which may be used for interactive sessions. The second is the
Signature HTTP Header, which is typically used by automated software
agents.
For high security transactions, having an additional signature on the HTTP
header allows a client to ensure that even if the transport channel has been
compromised, that the content of the messages have not been compromised.
This specification provides a HTTP Signature Header mechanism that can be
used by a client to authenticate the sender of a message and ensure that
particular headers have not been modified in transit.
There are a number of components in a signature that are common between the
'Signature' HTTP Authentication Scheme and the 'Signature' HTTP Header. This
section details the components of a digital signature.
The following section details the signature parameters.
REQUIRED. The `keyId` field is an opaque string that the server can use to look
up the component they need to validate the signature. It could be an SSH key
fingerprint, a URL to machine-readable key data, an LDAP DN, etc. Management
of keys and assignment of `keyId` is out of scope for this document.
REQUIRED. The `algorithm` parameter is used to specify the digital signature
algorithm to use when generating the signature. Valid values for this
parameter can be found in the Signature Algorithms registry located at
http://www.iana.org/assignments/signature-algorithms and MUST NOT be
marked "deprecated".
OPTIONAL. The `headers` parameter is used to specify the list of HTTP headers
included when generating the signature for the message. If specified, it
should be a lowercased, quoted list of HTTP header fields, separated by a
single space character. If not specified, implementations MUST operate as if
the field were specified with a single value, the `Date` header, in the list
of HTTP headers. Note that the list order is important, and MUST be specified in
the order the HTTP header field-value pairs are concatenated together
during signing.
REQUIRED. The `signature` parameter is a base 64 encoded digital signature,
as described in RFC 4648,
Section 4.
The client uses the `algorithm` and `headers` signature parameters to form a
canonicalized `signing string`. This `signing string` is then signed with the
key associated with `keyId` and the algorithm corresponding to `algorithm`.
The `signature` parameter is then set to the base 64 encoding of the signature.
If any of the parameters listed above are erroneously duplicated in the
associated header field, then the last parameter defined MUST be used. Any
parameter that is not recognized as a parameter, or is not well-formed,
MUST be ignored.
In order to generate the string that is signed with a key, the client MUST use
the values of each HTTP header field in the `headers` Signature parameter,
in the order they appear in the `headers` Signature parameter. It is out of
scope for this document to dictate what header fields
an application will want to enforce, but implementers SHOULD at minimum
include the request target and Date header fields.
To include the HTTP request target in the signature calculation, use the
special `(request-target)` header field name.
If the header field name is `(request-target)` then generate the header field
value by concatenating the lowercased :method, an ASCII space, and
the :path pseudo-headers (as specified in
HTTP/2, Section 8.1.2.3).
Create the header field string by concatenating the lowercased header field
name followed with an ASCII colon `:`, an ASCII space ` `, and the header
field value. Leading and trailing optional whitespace (OWS) in the header field
value MUST be omitted (as specified in
RFC7230,
Section 3.2.4).
If there are multiple instances of the same header field, all header field
values associated with the header field MUST be concatenated, separated by a
ASCII comma and an ASCII space `, `, and used in the order in which
they will appear in the transmitted HTTP message. Any other modification to
the header field value MUST NOT be made.
If value is not the last value then append an ASCII newline `\n`.
To illustrate the rules specified above, assume a `headers` parameter list
with the value of `(request-target) host date cache-control x-example` with
the following HTTP request headers:
GET /foo HTTP/1.1
Host: example.org
Date: Tue, 07 Jun 2014 20:51:35 GMT
X-Example: Example header
with some whitespace.
Cache-Control: max-age=60
Cache-Control: must-revalidate
For the HTTP request headers above, the corresponding signature string is:
(request-target): get /foo
host: example.org
date: Tue, 07 Jun 2014 20:51:35 GMT
cache-control: max-age=60, must-revalidate
x-example: Example header with some whitespace.
In order to create a signature, a client MUST:
Use the contents of the HTTP message, the `headers` value, and the
Signature String Construction algorithm to create the signature string.
The `algorithm` and key associated with `keyId` must then be used to
generate a digital signature on the signature string.
The `signature` is then generated by base 64 encoding the output of the
digital signature algorithm.
For example, assume that the `algorithm` value was "rsa-sha256". This would
signal to the application that the data associated with `keyId` is an
RSA Private Key (as defined in RFC 3447), the
signature string hashing function is SHA-256, and the signing
algorithm is the one defined in RFC 3447,
Section
Section 8.2.1. The result of the signature creation algorithm
specified in RFC 3447 should result in a
binary string, which is then base 64 encoded and placed into the
`signature` value.
In order to verify a signature, a server MUST:
Use the received HTTP message, the `headers` value, and the Signature String
Construction algorithm to recreate the signature string.
The `algorithm`, `keyId`, and base 64 decoded `signature` listed in the
signature parameters are then used to verify the authenticity of the
digital signature.
For example, assume that the `algorithm` value was "rsa-sha256". This would
signal to the application that the data associated with `keyId` is an
RSA Public Key (as defined in RFC 3447), the
signature string hashing function is SHA-256, and the `signature`
verification algorithm to use to verify the signature is the one defined in
RFC 3447, Section
Section 8.2.2. The result of the signature verification algorithm
specified in RFC 3447 should result in a
successful verification unless the headers protected by the signature were
tampered with in transit.
The "signature" authentication scheme is based on the model that the client must
authenticate itself with a digital signature produced by either a private
asymmetric key (e.g., RSA) or a shared symmetric key (e.g., HMAC). The scheme
is parameterized enough such that it is not bound to any particular key type or
signing algorithm. However, it does explicitly assume that clients can send an
HTTP `Date` header.
The client is expected to send an Authorization header
(as defined in
RFC 7235,
Section 4.1) where the "auth-scheme" is "Signature" and the
"auth-param" parameters meet the requirements listed in
Section 2: The Components of a Signature.
The rest if this section uses the following HTTP request as an example.
POST /foo HTTP/1.1
Host: example.org
Date: Tue, 07 Jun 2014 20:51:35 GMT
Content-Type: application/json
Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
Content-Length: 18
{"hello": "world"}
Note that the use of the `Digest` header field is per
RFC 3230, Section 4.3.2
and is included merely as a demonstration of how an implementer could include
information about the body of the message in the signature.
The following sections also assume that the "rsa-key-1" keyId refers to a
private key known to the client and a public key known to the server.
The "hmac-key-1" keyId refers to key known to the client and server.
A server may notify a client when a protected resource could be accessed by
authenticating itself to the server. To initiate this process, the server
will request that the client authenticate itself via a 401 response code. The
server may optionally specify which HTTP headers it expects to be signed
by specifying the `headers` parameter in the WWW-Authenticate header.
For example:
HTTP/1.1 401 Unauthorized
Date: Thu, 08 Jun 2014 18:32:30 GMT
Content-Length: 1234
Content-Type: text/html
WWW-Authenticate: Signature realm="Example",headers="(request-target) date"
...
The authorization header and signature would be generated as:
Authorization: Signature keyId="rsa-key-1",algorithm="rsa-sha256",
headers="(request-target) host date digest content-length",
signature="Base64(RSA-SHA256(signing string))"
The client would compose the signing string as:
(request-target): post /foo\n
host: example.org\n
date: Tue, 07 Jun 2014 20:51:35 GMT\n
digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=\n
content-length: 18
Note that the '\n' symbols above are included to demonstrate where the new
line character should be inserted. There is no new line on the final line of
the signing string.
For an RSA-based signature, the authorization header and signature would then
be generated as:
Authorization: Signature keyId="rsa-key-1",algorithm="rsa-sha256",
headers="(request-target) host date digest content-length",
signature="Base64(RSA-SHA256(signing string))"
For an HMAC-based signature without a list of headers specified, the
authorization header and signature would be generated as:
Authorization: Signature keyId="hmac-key-1",algorithm="hmac-sha256",
headers="(request-target) host date digest content-length",
signature="Base64(HMAC-SHA256(signing string))"
The only difference between the RSA Example and the HMAC Example is the
signature algorithm that is used. The client would compose the signing string
in the same way as the RSA Example above:
(request-target): post /foo\n
host: example.org\n
date: Tue, 07 Jun 2014 20:51:35 GMT\n
digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=\n
content-length: 18
The "signature" HTTP Header is based on the model that the sender must
authenticate itself with a digital signature produced by either a private
asymmetric key (e.g., RSA) or a shared symmetric key (e.g., HMAC). The scheme
is parameterized enough such that it is not bound to any particular key type or
signing algorithm. However, it does explicitly assume that senders can send an
HTTP `Date` header.
The sender is expected to transmit a header
(as defined in
RFC 7230,
Section 3.2) where the "field-name" is "Signature", and the "field-value"
contains one or more "auth-param"s (as defined in
RFC 7235,
Section 4.1) where the "auth-param" parameters meet the requirements
listed in Section 2: The Components of a Signature.
The rest if this section uses the following HTTP request as an example.
POST /foo HTTP/1.1
Host: example.org
Date: Tue, 07 Jun 2014 20:51:35 GMT
Content-Type: application/json
Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
Content-Length: 18
{"hello": "world"}
The following sections assume that the "rsa-key-1" keyId refers to a
private key known to the client and a public key known to the server.
The "hmac-key-1" keyId refers to key known to the client and server.
The signature header and signature would be generated as:
Signature: keyId="rsa-key-1",algorithm="rsa-sha256",
headers="(request-target) host date digest content-length",
signature="Base64(RSA-SHA256(signing string))"
The client would compose the signing string as:
(request-target): post /foo\n
host: example.org\n
date: Tue, 07 Jun 2014 20:51:35 GMT\n
digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=\n
content-length: 18
Note that the '\n' symbols above are included to demonstrate where the new
line character should be inserted. There is no new line on the final line of
the signing string.
For an RSA-based signature, the authorization header and signature would then
be generated as:
Signature: keyId="rsa-key-1",algorithm="rsa-sha256",
headers="(request-target) host date digest content-length",
signature="Base64(RSA-SHA256(signing string))"
For an HMAC-based signature without a list of headers specified, the
authorization header and signature would be generated as:
Signature: keyId="hmac-key-1",algorithm="hmac-sha256",
headers="(request-target) host date digest content-length",
signature="Base64(HMAC-SHA256(signing string))"
The only difference between the RSA Example and the HMAC Example is the
signature algorithm that is used. The client would compose the signing string
in the same way as the RSA Example above:
(request-target): post /foo\n
host: example.org\n
date: Tue, 07 Jun 2014 20:51:35 GMT\n
digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=\n
content-length: 18
&rfc2119;
&rfc4648;
&rfc6376;
&rfc7230;
&rfc7235;
&jwa;
&rfc2617;
&rfc3230;
&rfc3447;
&rfc5246;
&rfc6749;
There are a number of security considerations to take into account when implementing
or utilizing this specification. A thorough security analysis of this protocol,
including its strengths and weaknesses, can be found in
Security Considerations for HTTP Signatures.
This specification was designed to be simple, modular, and extensible. There
are a number of other specifications that build on this one. For
example, the
HTTP Signature Nonces
specification details how to
use HTTP Signatures over a non-secured channel like HTTP and the
HTTP Signature Trailers
specification explains how to apply HTTP
Signatures to streaming content. Developers that desire more functionality
than this specification provides are urged to ensure that an extension
specification doesn't already exist before implementing a proprietary
extension.
If extensions to this specification are made by adding new Signature
Parameters, those extension parameters MUST be registered in the
Signature Authentication Scheme Registry. The registry will be created and
maintained at (the suggested URI)
http://www.iana.org/assignments/http-auth-scheme-signature. An
example entry in this registry is included below:
Signature Parameter: nonce
Reference to specification: [HTTP_AUTH_SIGNATURE_NONCE], Section XYZ.
Notes (optional): The HTTP Signature Nonces specification details
how to use HTTP Signatures over a unsecured channel like HTTP.
The following test data uses the following RSA 2048-bit keys,
which we will refer to as `keyId=Test` in the following samples:
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDCFENGw33yGihy92pDjZQhl0C3
6rPJj+CvfSC8+q28hxA161QFNUd13wuCTUcq0Qd2qsBe/2hFyc2DCJJg0h1L78+6
Z4UMR7EOcpfdUE9Hf3m/hs+FUR45uBJeDK1HSFHD8bHKD6kv8FPGfJTotc+2xjJw
oYi+1hqp1fIekaxsyQIDAQAB
-----END PUBLIC KEY-----
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
All examples use this request:
POST /foo?param=value&pet=dog HTTP/1.1
Host: example.com
Date: Sun, 05 Jan 2014 21:31:40 GMT
Content-Type: application/json
Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
Content-Length: 18
{"hello": "world"}
If a list of headers is not included, the date is the only header that is
signed by default. The string to sign would be:
date: Sun, 05 Jan 2014 21:31:40 GMT
The Authorization header would be:
Authorization: Signature keyId="Test",algorithm="rsa-sha256",
signature="SjWJWbWN7i0wzBvtPl8rbASWz5xQW6mcJmn+ibttBqtifLN7Sazz
6m79cNfwwb8DMJ5cou1s7uEGKKCs+FLEEaDV5lp7q25WqS+lavg7T8hc0GppauB
6hbgEKTwblDHYGEtbGmtdHgVCk9SuS13F0hZ8FD0k/5OxEPXe5WozsbM="
The Signature header would be:
Signature: keyId="Test",algorithm="rsa-sha256",
signature="SjWJWbWN7i0wzBvtPl8rbASWz5xQW6mcJmn+ibttBqtifLN7Sazz
6m79cNfwwb8DMJ5cou1s7uEGKKCs+FLEEaDV5lp7q25WqS+lavg7T8hc0GppauB
6hbgEKTwblDHYGEtbGmtdHgVCk9SuS13F0hZ8FD0k/5OxEPXe5WozsbM="
The minimum recommended data to sign is the (request-target), host, and date. In
this case, the string to sign would be:
(request-target): post /foo?param=value&pet=dog
host: example.com
date: Sun, 05 Jan 2014 21:31:40 GMT
The Authorization header would be:
Authorization: Signature keyId="Test",algorithm="rsa-sha256",
headers="(request-target) host date", signature="qdx+H7PHHDZgy4
y/Ahn9Tny9V3GP6YgBPyUXMmoxWtLbHpUnXS2mg2+SbrQDMCJypxBLSPQR2aAjn
7ndmw2iicw3HMbe8VfEdKFYRqzic+efkb3nndiv/x1xSHDJWeSWkx3ButlYSuBs
kLu6kd9Fswtemr3lgdDEmn04swr2Os0="
A strong signature including all of the headers and a digest of the body of
the HTTP request would result in the following signing string:
(request-target): post /foo?param=value&pet=dog
host: example.com
date: Sun, 05 Jan 2014 21:31:40 GMT
content-type: application/json
digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
content-length: 18
The Authorization header would be:
Authorization: Signature keyId="Test",algorithm="rsa-sha256",
headers="(request-target) host date content-type digest content-length",
signature="vSdrb+dS3EceC9bcwHSo4MlyKS59iFIrhgYkz8+oVLEEzmYZZvRs
8rgOp+63LEM3v+MFHB32NfpB2bEKBIvB1q52LaEUHFv120V01IL+TAD48XaERZF
ukWgHoBTLMhYS2Gb51gWxpeIq8knRmPnYePbF5MOkR0Zkly4zKH7s1dE="
The Signature header would be:
Signature: keyId="Test",algorithm="rsa-sha256",
headers="(request-target) host date content-type digest content-length",
signature="vSdrb+dS3EceC9bcwHSo4MlyKS59iFIrhgYkz8+oVLEEzmYZZvRs
8rgOp+63LEM3v+MFHB32NfpB2bEKBIvB1q52LaEUHFv120V01IL+TAD48XaERZF
ukWgHoBTLMhYS2Gb51gWxpeIq8knRmPnYePbF5MOkR0Zkly4zKH7s1dE="
The editor would like to thank the following individuals for feedback on and
implementations of the specification (in alphabetical order): Stephen Farrell,
Phillip Hallam-Baker, Dave Lehn, Dave Longley, James H. Manger,
Mark Nottingham, Yoav Nir, Julian Reschke, and Michael Richardson.
The following entry should be added to the Authentication Scheme Registry
located at
http://www.iana.org/assignments/http-authschemes
Authentication Scheme Name: Signature
Reference: [RFC_THIS_DOCUMENT], Section 2.
Notes (optional): The Signature scheme is designed for clients to
authenticate themselves with a server.
The following initial entries should be added to the Signature Algorithm
Registry to be created and maintained at (the suggested URI)
http://www.iana.org/assignments/signature-algorithms:
Editor's note: The references in this section are problematic as many of the
specifications that they refer to are too implementation specific, rather
than just pointing to the proper signature and hashing specifications. A
better approach might be just specifying the signature and hashing function
specifications, leaving implementers to connect the dots (which are not that
hard to connect).
Algorithm Name: rsa-sha1
Reference: RFC 6376, Section 3.3.1
Status: deprecated
Algorithm Name: rsa-sha256
Reference: RFC 6376, Section 3.3.2
Status: active
Algorithm Name: hmac-sha256
Reference: HS256 in
JOSE JSON Web Algorithms, Section 3.2
Status: active
Algorithm Name: ecdsa-sha256
Reference: ES256 in
JOSE JSON Web Algorithms, Section 3.4
Status: active